Synchronized pulse communication system



Aug. 10, 1948.

e. w. FY-LER 2,446,819

SYNCHRONIZED PULSE COMMUNICATION SYSTEM Filed March 27', 1943TRANSMITTER rms DELAY 86*" ozvlca TIMEDELAY DEVICE CONVERTER DETECTOAMPLIFIER LOC OSCILL 0R Inventor George W. Fyler,

y His Attorney.

Patented Aug. 10, 1948 2,446,819 SYNCHRO-N-IZED PULSE COMMUNICATION STEMGeorge W. Fyler, Stratford', Conn assignor to General Electric Company,a corporation of New York Application March 27, 1943, SerialNo; 480,823

6' Claims. (01. 250--'-13') My invention relates to pulse systems ofcommunication.

Pulse systems are advantageous for the. transmission of speech, music,and other forms of. intelligence, because the effect of extraneouselectric fields, noise, etc., which may affect the receiving apparatus,may be reduced by rendering the receiving means inoperative during theintervals between pulses. Moreover, by width or frequency modulating thepulses of radio frequency carrier, limiting means may be employed toeliminate, or at least substantially reduce, the amount of noise voltageappearing on the received pulses. Moreover, for a given average power,it is possible to operate the transmitting oscillator electron dischargedevices or tubes at high instantaneous powers and, consequently, highefiiciencies. It isv therefore, an object of my invention to provide anew and improved radio communication, system of the pulse type.

Another object of my invention is to. provide a new and improved methodand'meansfor reception in which the effects of undesired impulses,extraneous influences, etc. are reduced or eliminated.

The utilization of pulse communication systems makes possible duplex ormultiplex operation on one frequency whereby two or moredifferent'conlversations or transmissions of signals may be conducted onone frequency at the same time without interference. It is anotherobject of my invention to provide a new and improved system for duplexor multiplex operation.

It is still another object of my invention to provide a duplex ormultiplex system in which im.- pulses may be transmitted only when nosignal is being received.

Another object of my invention is to provide in duplex or multiplexsystems, means for synchronizing the times of transmission of. thevarious transmitting means.

The novel features which I believe to-be characteristic of my inventionare-set forth with particularity in the appended claims. Myinventionitself, however, both as to its organization method of operationtogether with further ob jects and advantages thereof may best beun'derstood by reference to the following description taken inconnection with the accompanying draw ing in which Fig. 1 representsschematicallya circuit embodying the principlesof my invention; Fig. 2shows a modified form ofreceiver which may be substituted for thereceiver shown in Fig. 1; and Fig. 3 shows inblock form an adapta- 2tion of the principles ofmy invention to a multipl'ex'system of radiocommunication;

In Fig; 1, thereis shown an embodiment of my invention permitting duplexor multiplex communication on a single band of frequencies. Means isprovided whereby pulses are transmitted only during the intervalsbetweenreceived pulses.

At each'station in the system, there is provided a suitable" transmitterEilfiand. a suitable receiver 5!;

The transmitter may comprise asawtoot'h wave generator 52, illustratedin the form of a multivibrator of the floating cathode type, maycomprise electron discharge devices ll and l' 2 having anodesl3', M,control electrodes 15,16 and the cathodes", 18, respectively. Acathodebiasing resistor 19 is provided between the cathodes and ground.The capacitor is connected between the'anode 1-3 and the controlelectrode 16. A capacitor 8! and'a resistor 82 are connected in seriesbetween the anode l4 and ground; The control electrodes are connected toground by suitable resistors 9T and 98. Anode potential is 16 to. becomenegative and the discharge device 12 is rendered non-conductive.Thecapacitor 8 tends to'become charged when the device 12 isnon-conductive because of the high potential thenexisting on anode '14.The charge on capacitor 80, which accumulated during the precedinginterval tends to leak off through the resistance. 98

and the control electrode 16. gradually becomes less negative andfinally becomes sufiiciently lessnegative to permit the device 12 toconduct current. Such conduction causes currentto flow through theresistance 19' and drives the cathode l1 slightly more positive withrespect to the control electrode 15 and thereby causes. a reduction ofthe anode current through the device 1 L The result is; an increase'inthe positive potential on the anode 13' which drives the controlelectrode 16 of the device 74 slightly more positive toin-- crease thecurrent through the discharge device 12. The current in the resistance19. again increases. This increase continues until the discharge. deviceH is cut on". The condenser 8| of the sawtooth wave, the stored energyis released suddenly by the condenser 58 and the inductance 59 at arelatively high potential to the anode SI of the oscillator 62. leaseprovides a pulse of high intensity, short du- The sudden re=.

vices 88 and 89. relative widths of the positive and negative squarecondenser 8|. Thus, it may be considered that the transmitter isrendered inoperative when pulses are to be received or that thetransmitter is rendered operative for the transmission of pulses only atpredetermined times between the receipt of pulses from a remotetransmitter.

In order to adjust the time interval between the positive and negativeimpulses impressed on the control electrode '15 there is provided means93 comprising a, potentiometer type resistance connected between thecontrol electrodes of the de- This causes variation of the blockswithout appreciably changing the frequency. Ifthe repetition rate ofpulses in the multivibrator '52 of the transmitter and the quenchfrequency of the receiver are chosen relaration, radio frequency energywhich is trans;

mitted over the antenna 63 to the remote receiver. Suitable modulationmeans may be employed as indicated by the numeral 60. The amplitude ofthe sawtooth wave of plate current in the discharge device 5'! may becontrolled or varied by the potential of a second control electrode I00of the device 51. The discharge of the device 51 is dependent not onlyon the waves impressed thereon by means of the control electrode 56 butalso by the potential of the second control electrode I 00. In thismanner a simple modulator of the Heising type may be used for modulatingthe potential of the control electrode I00 in accordance with audiomodulation frequencies. It is apparent that the pulse rate should behigher than the highest modulating frequency.

The lower portion of Fig. 1 illustrates a suitable periodicallyapertured receiver which may be of the super-regenerative type with aself-quench rate which is nearly the same as the repetition rate of themulti-vibrator. Signals received on the antenna 64 are reproduced by anydesired means including a loudspeaker 65.

Means is rovided to synchronize the transmission and reception of pulsesfrom any one station so that pulses are not transmitted during theperiod of reception of pulses. This means may comprise a suitable timedelay device 86,

connected between the anode 06 of the detector 61 and the controlelement of the discharge device H of the sawtooth wave generator. Anegative impulse appearing on the anode 66 of the detector isdifferentiated in a suitable filter 8! to remove audio components of theanode voltage and is impressed on the time delay circuit 85. The timedelay circuit illustrated is in the form of a multivibrator, andincludes electron discharge devices 88 and 89. The differentiated pulsesfrom the receiver are impressed on the control electrode 90 of device83. Relatively square pulses appear in the anode circuit as indicated inthe drawing. These pulses are'differentiated in suitable filter sections9! and 92 and the sharp, differentiated pulses, the shape of which isindicated at the output of the filter sections, are impressed on thecontrol electrode 15 of the discharge device ll in the sawtooth wavegenerator of the transmitter.

Inasmuch as the discharge device H is normally conducting, theappearance of positive pulses on the control electrode usually has noeffect and the generator continues to generate sawtooth waves. However,the receipt of negative pulses drives the control electrode 15sulficiently negative to cut off the discharge device H and interruptthe production of sawtooth Waves by causing discharge device (2 todischarge system'is appreciably increased. 1

tively-close together, as, for example, 1000 cycles per second and 990cycles per second respectively, the receiver and transmitter will tendto pull into synchronism in such a manner that the local transmitterwill emit pulses at a definite time during the intervals between thereceipt of pulses from the distant stations. Of course, thesefrequencies should normally be higher than the highest modulatingfrequency, as previously pointed out above. Therefore these values aremerely illustrative. For voice communication purposes, these frequenciesmight be at least 5,000 to 10,000 cycles per second to insure goodintelligibility.

In order to adjust the repetition rate of the sawtooth wave generator52, the resistances and 98 may be made variable. In a similar manner, inorder to adjust the repetition rate of the multivibrator 86 in the timedelay circuit associated with both the transmitter and the receiver, aresistance 94 of the variable type may be connected between the positiveterminal of the source of potential 95' and a point on the potentiometer93. The quench rate of the receiver may be adjusted to the desiredfrequency by providin a variable resistor 95 shunted by a suitablecapacitance 99 in the grid-to-cathode circuit.

By proper choice of constants in the time delay circuits, the systemautomatically locks in such a way that the receiver synchronizes withthe remote transmitter, and the local transmitter synchronizes with thelocal receiver by means of 50 the time delay device. The remote receiverlocks in with the local transmitter and the remote transmitter thensynchronizes or looks in with the remote receiver. a

The provision of the time delay circuits, and

the adjustment device or means 93, enables adtion of the system willtake place because the transmitter in one station will synchronize thereceiver at the distant station, the distant receiver will lock-in thedistant transmitter and the local receiver will then lock in with thedistant transmitter. In this way a double lock is provided which willinsure proper operation of the system even if only one end of the systemis working properly and, accordingly, the reliability of It has beenstated that a superheterodyne type the each station including a controlpulse generator, each of said pulse generators having substantially thesame free-running repetition rate, a superregenerative receiver at eachof said stations having a quench rate substantially equal to'saidpredetermined repetition rate, each of said receivers automaticallysynchronizing with the other of said transmitters, and adjustable timedelay means at each of said stations responsive to recelved pulses atthe same station for developing synchronizing pulses recurring at saidrepetition rate but delayed by a selectable time interval, and means forsynchronizing the pulse generator at the same station with said delayedpulses, there'- by to insure that pulses are transmitted from eachstation only in the intervals between reception of pulses at the samestation, said time delay intervals being adjusted to cause thetransmitters and receivers at both said stations to be mutually lockedin synchronism in a closed loop to operate at said repetition rate.

5. A pulse communication system comprising a plurality of variablyspaced stations, a pulse transmitter at each station including a pulsegenerator, each said pulse generator having substantially .the samepredetermined repetition rate, a periodically operative receiver at eachstation apertured at a rate substantially equal to 'said repetitionrate, each said receiver being arranged to synchronize with any one ofsaid transmitters, a multivibrator at each of said stations connectedfor synchronization by pulses received at the same station, each saidmultivibrators being connected to synchronize the local pulse generatorwith pulses received at the local receiver so that pulses aretransmitted from any station only at discrete interval betweenireceivedpulses, and means for varying the on-ofi ratio of said multivibratorthereby to var the time interval between received and transmitted pulsesat any one station in accordance with the spacing between said stations.

6. In a pulse communication system including a pair of spaced stations.a pulse transmitterin each of said stations, a control pulse generatorfor causing each of said transmitters to radiate discrete pulses at thepulse frequency of said generator, each said generator being adapted tobe synchronized for operation at a common pulse frequency, a pulsereceiver in each of said stations, means for synchronizing each receiverwith pulses from the transmitter at the other station and for renderingsaid receive operative only during short time intervals including saidpulses, and adjustable time delay means controlled by received pulsesfrom each receiver for impressing synchronizing pulses on the controlpulse generator at the same station after a selectable time delay;"thereby to restrict radiation of pulses from each station to discreteintervals between reception of pulses at the same station, said timedelays being adjusted to cause the transmitters and receivers at bothsaid stations to be mutually locked in synchronism in a closed loop tooperate at said common pulse frequency.

' GEORGE W. FYLER.

REFERENCES CITED The following references are of record fileof thispatent:

UNITED STATES PATENTS FOREIGN PATENTS Country Date Great Britain May 22,1930 in the Number Number

